A seat slide device for vehicle seat has a basic structure in which an upper rail fixed to a seat is slidably engaged with a lower rail which is fixed to a vehicle floor to extend in the forward/rearward direction. This seat slide device is motorized by supporting a motor-driven screw rod on one of the upper and lower rails to extend in a direction of extension thereof in a manner to allow the screw rod to rotate and by fixing a nut member which is screwed onto a nut screwing portion of the screw rod to the other of the upper and lower rails.
The screw rod is rotatably supported between a gear box which is installed at an end (usually the front end) of one of the upper and lower rails and a bearing installed at the rear end of this one of the upper and lower rails. In addition, a load transmitting member (load transmitting bracket), which supports the screw rod in a manner to allow the screw rod to rotate and prevent load caused upon a collision from being transmitted directly to the gear box by dispersing the load, is fixed to the rail which supports the screw rod.